1. Field of the Invention
The present invention relates to a battery outer case that houses a flat battery pack such as, for example, a laminate cell battery, etc., composed of a plurality of thin batteries laminated one over another.
2. Description of the Related Art
As a battery outer case in which this kind of flat battery pack is housed, there can be considered such a one as shown in FIGS. 4A through 4F.
Specifically, a battery outer case 100 shown in FIG. 4A includes a metal container main body 102 in which a flat battery pack 101 is housed therein, and a metal lid 103 that serves to close an opening formed in the metal container main body 102. An outwardly protruding connection flange 104 is formed at an open end of the metal container main body 102, and a connection flange 105, similarly protruding outwards, is formed on an end portion of the metal lid 103, with the respective connection flanges 104, 105 being superposed and coupled with each other by means of spot welding or caulking. As such a caulking technique, there can be used eyelets, so-called TOX (a registered trademark of TOX PRESSOTECHNIK Co., Ltd.) joints, etc.
In FIG. 4B, a metal container main body 102 is formed at its open end with a joint piece 106 extended upwards therefrom for connection, and a metal lid 101 is also formed on its outer periphery with an upwardly extending joint piece 107, the joint pieces 106, 107 being superposed and coupled with each other by means of spot welding or caulking.
In the jointing or coupling techniques as shown in FIG. 4A and FIG. 4B, however, there is the following problem. That is, in any case of spot welding and caulking joint, it is necessary for the joint pieces 106, 107 of the connection flanges 104, 105 to have their widths X1, Y1 of at least 7 to 10 mm as a welding margin or a caulking margin, and hence the occupation space thereof becomes accordingly large.
Thus, as shown in FIG. 4C and FIG. 4D, it is considered that an edge of a metal lid 103 is placed in abutment with a corresponding edge of a metal container main body 102 while eliminating the above-mentioned connection flanges and joint pieces, and abutment portions 108 of the metal lid 103 and the metal container main body 102 are joined with each other by laser welding (for example, Japanese patent application laid-open No. 2004-14125).
In such a case of abutment joint or connection, however, spatter generated upon welding can be easily dispersed into the inside of the container, and heat can also be transmitted to the inside of the container, so the flat battery pack 101 is liable to be damaged. In particular, in the case of a thin battery with its exterior being formed of a laminate film, the laminate layer can be damaged to induce a reduction in electrical insulation.
FIG. 4E shows an example in which a metal container main body 102 and a metal lid 103 are coupled with each other by means of bolts 109. In this example, each bolt 109 has its bolt shaft portion 109a inserted into a bolt hole formed in the metal lid 103, and its bolt head 109b engaged with the metal lid 103, with an end of the bolt shaft portion 109a being threaded into a bottom plate portion 102a of the metal container main body 102.
In this case, however, there arises another problem. That is, the bolt head 109b of each bolt 109 projects from an upper surface of the metal lid 103, so the occupation space of the entire apparatus is accordingly increased by the height of each bolt head 109b, and at the same time, the entire weight thereof is also increased by the weight of all the bolts 109.
In addition, it can be further considered that a caulking structure used in a cylindrical battery or the like is employed, as shown in FIG. 4F. This caulking structure is such that a lid body 203 is inserted into the inner periphery of an open end portion of a metal container main body 201 through a ring-shaped gasket 202, and is then fixedly secured to the metal container main body 201 by caulking or bending the open end portion thereof inwardly.
In the case of such a caulking structure, however, the gasket 202 is needed as an additional part, resulting in an increase in the number of required parts.